The present invention relates generally to subscription television signal decoders and, more particularly, to an improved homing system for automatically tuning a subscription television signal decoder which has been placed in an "off-mode" by a subscriber to a subscription television channel for receiving current subscriber authorization data.
In subscription television systems, television signals are typically transmitted to system subscribers in a scrambled form either along a coaxial cable or as an "over-the-air" broadcast. Each subscriber is provided with a decoder operable for unscrambling the subscription television signals, which unscrambeled signals are supplied to a conventional television receiver for viewing. Quite often, the decoders are of the multi-channel variety wherein subscription television signals transmitted over a plurality of television channels may be selectively tuned by a conventional subscriber operated tuning system before being applied to the unscrambling circuits. In such cases, the subscription television signals are frequently grouped into a number of levels or tiers each representing a different programming category such as sporting events, movies, etc., with the decoder of a particular subscriber being authorized for decoding or unscrambling the televised subscription programming signals in selected categories, the televised subscription programming signals in the remaining unauthorized categories being coupled on the television receiver in a scrambled and unviewable form. Of course, in such a system, all of the subscription television signals will be reproduced in a scrambled and unviewable form by a normal television receiver.
In a tiered subscription television system as described above, each system subscriber may selectively subscribe to one or more of the programming tiers as his or her interests dictate. To this end, each decoder, which is uniquely identified by a stored subscriber address code, includes a subscriber authorization register storing a subscriber authorization code identifying the program tiers which the subscriber is authorized to decode. The stored subscriber authorization code is compared to a program code typically transmitted during a selected horizontal line of the vertical intervals of a tuned subscription television signal, the program code identifying the programming level or tier of the accompanying television signal. If the stored subscriber authorization code and the broadcast program code result in a favorable comparison, suitable decode authorization signals are developed in the decoder enabling the received television signal to be decoded and coupled to the subscriber television receiver for viewing. On the other hand, if a proper match between the subscriber authorization code and the transmitted program code is not detected, indicating that the subscriber is not authorized to decode television signals in the programming tier identified by the broadcast program code, the decode authorization signals are not developed and the received television signal is not unscrambled by the decoder.
From time to time, it is necessary to update or refresh the stored subscriber authorization codes to reflect changes in the programming status of the subscribers, to completely de-authorize delinquent subscribers or, for example, to selectively authorize the decoding of special event or premium programs. Such updating or refreshing operations are typically accomplished by sequentially addressing the system decoders for entering the updated subscriber authorization codes during one or more horizontal lines of the vertical intervals of the broadcast subscription television signals. Since a relatively long period of time may be required to address all of the decoders in the system, it has been found convenient to at least partially execute the memory refreshing operation at night while the decoders are turned off. To facilitate such, much of the circuitry of the decoders, including the tuning system thereof, is maintained in an operational status even though the decoder is ostensibly turned off by the subscriber. In addition, steps must be taken to insure that, upon being turned off by a subscriber, the decoder tuner reverts or homes to a television channel through which subscription television signals are being transmitted and not to a channel used for transmitting normal un-encoded television signals. In the past, decoders have been designed such that their tuning systems would automatically home to a selected one of a limited number, e.g. four, of pre-programmed homing channels. Therefore, by selecting a pre-programmed homing channel which is also a subscription channel, the operator of the subscription system can insure that the tuning system of the decoder will home to a television channel enabling the decoders to be suitably refreshed when placed in an off-mode by the subscriber.
While such limited pre-programmed homing channel systems generally provide adequate flexibility, they are subject to a number of major disadvantages. Initially, there is the time and expense of selecting and pre-programming each decoder supplied to a system subscriber. Also, and perhaps more importantly, it is quite possible that the system operator might not be using any of the pre-programmed homing channels as a subscription channel in which case the tuning systems of each decoder must be custom programmed for the particular application. This leads to additional costs and represents a highly undesirable situation.
It is therefore a basic object of the present invention to provide an improved homing system for a subscription television signal decoder.
It is a more specific object of the invention to provide a homing system for a subscription television signal decoder which automatically homes or reverts to a subscription television channel when the decoder is placed in an off-mode of operation.